1. Field of the Invention
This invention relates to a photocurable composition which is adapted for use as a photoresist or in image recording and which undergoes a curing reaction at high sensitivity by application of visible light or near infrared light.
2. Description of the Related Art
Hitherto known photocurable compositions which have high sensitivity to visible light are those which comprise the following types of initiators, e.g., composite initiators of dyes and aliphatic amines (Japanese Patent Publication No. Sho 44-20189), initiators of hexaarylbiimidazoles, radical generators and dyes (Japanese Patent Publication No. Sho 45-37377), initiators of hexaarylbiimidazoles and p-dialkylaminobenzylidene ketones (Japanese Patent Laid-open No. Sho 47-2528), initiators of cyclic-cis-.alpha.-dicarbonyl compounds and dyes (Japanese Patent Laid-open No. Sho 48-84183), initiators of carbonyl compounds and tertiary amines (Japanese Patent Laid-open No. Sho 52-134692), initiators of substituted triazines and merocyanine dyes (Japanese Patent Laid-open No. Sho 54-151024), initiators of biimidazoles and indanones (Japanese patent Laid-open No. Sho 54-155292), initiators of hexaarylbiimidazoles and p-dialkylaminostilbene derivatives (Japanese Patent Laid-open No. Sho 57-21401), initiators of hexaarylbiimidazoles and p-dialkylaminocinnamylidene derivatives (Japanese Patent Laid-open No. Sho 58-19315), initiators of triazine derivatives and Cyanine dyes (Japanese Patent Laid-open No. Sho 58-29803), initiators of triazine derivatives and thiapyrylium salts (Japanese Patent Laid-open No. Sho 58-40302), initiators of hexaarylbiimidazoles and n-dialkylstilbene derivatives or p-dialkylaminophenylbutadienyl derivatives and thiole compounds (Japanese Patent Laid-open No. Sho 59-56403), initiators of ketone-substituted derivatives and organic peroxides (Japanese Patent Laid-open No. Sho 60-32801), initiators of .alpha.-diketones and mercapto carboxylic acids (Japanese Patent Laid-open No. Sho 61-258802), initiators of .alpha.-diketones and polysulfides (Japanese Patent Laid-open No. Sho 61-258803) and the like.
The curing with visible light with a long wavelength has been reported as follows.
According to the Japanese Patent Publication No. Sho 44-20189, the degree of the curing is expressed in terms of a relative minimum exposure. EQU Relative minimum exposure=I.times.t
where I is an intensity of the light and t is a time before commencement of polymerization, and EQU log I=log 100-D
where the value of 100 is an intensity of carbon arc light for convenience's sake and D is a wedge density. Thus, EQU I=antilong (2-0.05n)
wherein n is the number of polymerization steps.
The relative minimum exposure of photocurable compositions in the Publication No. Sho 44-20189 is 31.7 for a composition having a maximum absorption wavelength of 430 nm, 63.1 for a composition having a maximum absorption wavelength of 575 nm, and 1000 for a composition having a maximum absorption wavelength of 680 nm. More particularly, the photocurable composition set out in the Publication No. Sho 44-20189 requires greater energy since it is cured at a longer wavelength.
In the Japanese Patent Laid-open No. Sho 58-29803, the degree of curing is indicated by the use of stepped tablets. According to the invention disclosed in Laid-Open No. Sho 58-29803, there is obtained a photocurable composition with a maximum of twelve steps of sensitivity by irradiation with light at 436 nm for 60 seconds, a photocurable composition with a maximum of eight steps of sensitivity by irradiation with light at 490 nm for 60 seconds, and a photocurable composition with a maximum of six steps of sensitivity by irradiation with light at 600 nm for 120 seconds. More particularly, since the compositions are cured with long wavelength visible light, greater energy is required.
For practical use, there is a high demand for photocurable compositions which are able to be cured at lower energy. Especially, there is a demand for a photocurable composition which is cured by application of long wavelength visible light or near infrared light at a similar low level of energy as that required by a photocurable composition capable of being cured with visible light having a shorter wavelength.